Drafting machine



1951 A. L. BAKER 2,996,805

DRAFTING MACHINE Filed March 25, 1957 2 heats-Sheet 1 Fig. I

INVENTOR ALL/STER L. BAKER AT RNEY Aug. 22, 1961 Filed March 25, 1957 A.L. BAKER DRAFTING MACHINE 2 Sheets-Sheet 2 INVENTOR.

ALL/STEP L. BAKER BY gw A ORNEY United States Patent-O 2,996,805 D GMACHINE Allister L. Baker, Denville, N.J., assignor to Keutfel &.lIisser Company, Hoboken, N1, a corporation of New ersey Filed Mar. 25,1957, Ser. No. 648,191 2 Claims. (CI. 33-79) This invention relates to acounter-balance construction for a drafting machine. The invention maybe used with a drafting machine of the pulley and band type. As is knownin the art, this type of drafting machine includes a fixed member whichmay be clamped to a drawing board, a first movable arm pivoted at oneend to the fixed member, a second movable arm pivoted at one end to themovable end of the first arm and a drafting head carried at the free endof the second movable arm and movable over the drawing board. Thedrafting head includes a protractor and a protractor arm with means forholding one or more scales, rulers or straightedges which can be rotatedabout the protractor. As the drafting head is moved over the drawingboard some member of the drafting head is maintained in orientation by acombination of pulleys and bands or parallelograms or the like. Whensuch a drafting machine is used on an inclined drawing board, it isnecessary to counter balance the movable parts so that the drafting headwill remain in any position in which it is placed over the surface ofthe drawing board. Suitable means have already been devised for counterbalancing the first movable arm so that it will not move under theaction of gravity with respect to the member clamped to the drawingboard. The present invention relates specifically to counter balancingmeans for the second movable arm which prevents it from moving under theaction of gravity with respect to the first movable arm when thedrafting machine is used on' an inclined board.

. The invention and the means for its attainment will be more .fullyunderstood after reading the following description taken in conjunctionwith the drawing in which:

FIG. I is a view in perspective showing the complete drafting machine.

FIG. II is a view in sectional elevation taken through the elbow betweenthe first and second movable arms, the two arms having been pivoted withrespect to each other at the elbow from the position shown in FIG. I toa position in which the second movable arm lies directly under the firstmovable arm.

FIG. III is a view in plan which is partly in section; the section beingalong the line IIIIII of FIG. II and looking in the direction of thearrows.

Referring to FIG. I, the anchor 2 or member which may be fastened to thedrawing board is provided with suitable clamp screws 4 for clamping iton a drawing board. The first movable arm 6 is pivoted to the anchor 2at one end as shown. The second movable arm 8 is pivoted to the otherend of the first movable arm 6 at the elbow which is shown in greaterdetail FIGS. II and III. The drafting head 10 is mounted at the free endof the second movable arm 8. The drafting head 10 includes a protractor12. which may be secured to a member within the drafting head 10 whichmember is maintained in orientation with respect to the drawing board bymeans of bands passing within the tubular portions of the arm 6 and 8.The protractor arm 14 is pivoted about the center of the drafting head10 so that the protractor arm 14 may be adjusted to any angular positionas indicated by the protractor 1'2. In the embodiment shown, theprotractor arm 14 carries two scales '16 and 18 which are detachablysecured to the protractor arm 14 by conventional means.

Patented Aug. 22, 1961 Referring to FIG. II the end bracket 20 of thefirst movable arm 6 is secured to the tubes 22 and 24 within which theband 26 is free to move. The band 26 passes around the elbow pulley 28and thereby maintains the elbow pulley 28 in orientation with respect toa fixed pulley which is secured to the anchor 2 and is mounted withinthe end bracket 21 FIG. I at the opposite end of the first movable arm6. The elbow pulley 28 carries a shaft 30 to which are secured the innerraces of the ball bearings 32 and 34 by means of the nut 36. The pulley28 is provided with a recess formed between the rim of the pulley andthe hub of the pulley. The outer race of the ball bearing 32 is pressedinto the end bracket 20 of the first movable arm 6 so that the arm 6 canpivot with respect to the pulley 28. Similarly, the outer race of theball bearing 34 is secured to the end bracket 38 of the second movablearm 8. The button 40 which helps to hold the outer race of the ballbearing 34 in the bracket 38 may also act as a slide for the elbow ofthe drafting machine as it moves over the surface of the drawing board.The band 42 passes around the pulley 28 and through the tubes 44 and 46of the second movable arm 8. This band 42 also passes around a pulleywithin the drafting head and maintains that pulley in orientation withrespect to the drawing board.

An eccentric drum or cam 48 is mounted within the end bracket 38 underthe pulley 28 and partially extending into the recess formed between thehub and rim of the pulley as shown. This eccentric drum 48 is providedwith an integral lower flange which is slotted to receive the key 50which is formed integrally with the end bracket 38. An integrally castlug projects downward from the flange on the eccentric drum 48 in thediametrically opposite position. This lug is internally threaded asshown to receive the adjusting screw 52. The adjusting screw 52therefore serves to adjust the eccentricity of the eccentric drum 48with respect to the axis of the pulley 28.

A leaf spring 54 (FIG. III) which may be built up of several strips asshown is carried by the elbow pulley 28 (i.e., by the member maintainedin orientation) and is always held thereby on the bottom side of theeccentric drum 48 (when the board is inclined) so that it always exertsa vertical upward force on the drum 48. (Vertical as used in thisparagraph means a direction parallel to the inclined drawing board in avertical plane perpendicular to the surface of the drawing board.) Oneend of the leaf spring 54 is pivotally attached to the under side of thedrum 28 by a pin 56 extending downward from the flange of the drum 28.The other end of the leaf spring 54 is restrained by a pin 58 which ismounted similarly in the drum 28. The central portion of the leaf spring54 engages the eccentric drum 48. The construction is such that theeccentricity of the eccentric drum is adjusted in the longitudinaldirection of the second movable arm. Thus, when the second movable armis vertical the eccentricity of the drum is in the vertical directionand when the second movable arm is horizontal, the eccentricity of thedrum is in the horizontal direction. For intermediate inclined positionsof the second movable arm, the eccentricity is in an inclined directionso that when the second movable arm is vertical the horizontal componentof the eccentricity is zero and increases gradually to a maximum whenthe second movable arm is pivoted from the vertical to the horizontalposition. The leaf spring 54 being carried by the member maintained inorientation exerts a force against the eccentric drum 48 which is alwaysupward and substantially vertical and constant. The moment of this forceabout the elbow depends on the horizontal component of the eccentricityof the eccentric drum 48 and therefore varies with the eccentricity fromzero to a maximum as 3 the second movable arm is pivoted from a verticalto a horizontal position.

The moment of force discussed above counterbalances the moment about theelbow of gravity acting on the second movable arm and the drafting head.Obviously, the moment arm of the force of gravity is also zero when thesecond movable arm is vertical and is a maximum when the second movablearm is horizontal. Thus the moment of the leaf spring acting on theeccentric drum can be made to counterbalance the moment of the force ofgravity for all angles of the second movable arm pivoting about theelbow.

The magnitude of the eflect produced by the force of gravity will alsodepend on the inclination of the drawing board. The eccentricity of theeccentric drum 48 may be adjusted to provide sufficient counterbalancingefiect for the inclination of the drawing board within the limits of anyparticular construction. The counterbalancing effect will be assisted tosome extent by forces of friction so that as a practical matter anyconstruction according to the present invention will be operative oversome range of board angles without readjustment.

Having thus described the invention, what is claimed is:

l. A counterbalance for the lower arm of a drafting machine having upperand lower arms pivoted together, the upper arm being pivoted to ananchor and the lower arm pivoted to the un-anchored end of the upperarm, an orienting member rotatably connected to the pivot between saidupper and lower arms, a leaf spring mounted by at least one of its endson said orienting member, a cam mounted on said lower arm and projectinginto engagement with said leaf spring, said cam being mounted formovement relative to said lower arm and substantially in the plane ofsaid lower arm so that said cam may be concentric'with said pivotbetween said upper and lower arms or may be eccentric relative thereto,said leaf spring being biased into engagement with said cam, meansconnected to the cam and accessible from the exterior of said lower armto control the degree of eccentric relation of said cam to said pivot,said counterbalance providing for adjusted balanced movement of saidlower arm whereby the counterbalancing effect between said leaf springand said cam will be a maximum when said lower arm is in a horizontalposition and will be a minimum when said lower arm is in a verticalposition, the counterbalancing effect of said spring and said cam andthe friction between said spring and said cam always maintaining thelower arm in proper counterbalancing relation.

2. A counterbalance for a drafting machine having a first and second armpivoted together and the first arm pivoted to an anchor, a pulleyrotatably connected to the pivot between said first and second arms,said pulley having a circumferential recess in the side adjacent saidsecond arm, a lead spring in said recess and mounted by at least one ofits ends on the pulley adjacent the rim thereof, an eccentric mounted onsaid second arm and located in said recess in a radial plane includingthe pivot and said leaf spring and having the periphery of saideccentric engageable with an intermediate portion of said leaf springdeflecting said intermediate portion of said leaf spring radially fromsaid pivot, said eccentric being mounted for movement relative to saidsecond arm and substantially in the plane of said second arm so thatsaid eccentric may be concentric with said pivot between said first andsecond arms or may be eccentric thereto, said leaf spring biased intoengagement with said eccentric means connected to the eccentric andaccessible from the exterior of said second arm to control the degree ofeccentricity of said eccentric relative to said pivot, saidcounterbalance providing for adjusted balanced movement of said secondarm whereby the counterbalancing effect between said leaf spring andsaid eccentric will be a maximum when said second arm is in a horizontalposition and will be a minimum when the second arm is in a verticalposition, the counterbalancing effect of said spring and said eccentricand the friction between said spring and said eccentric alwaysmaintaining the second arm in proper counterbalancing relation.

References Cited in the file of this patent UNITED STATES PATENTS2,266,765 Keuifel Dec. 23, 1941 2,362,050 Cole Nov. 7, 1944 2,374,020Ketting Apr. 17, 1945 2,552,335 Little May 8, 1951

